Old English leaf "leaf of a plant; page of a book," from Proto-Germanic *laubaz (cognates: Old Saxon lof, Old Norse lauf, Old Frisian laf, Dutch loof, Old High German loub, German Laub "foliage, leaves," Gothic lauf), perhaps from PIE *leup- "to peel off, break off" (cognates: Lithuanian luobas, Old Church Slavonic lubu "bark, rind"). Extended 15c. to very thin sheets of metal (especially gold). Meaning "hinged flap on the side of a table" is from 1550s.